Balancing Database Load Across Hosts

A NuoDB database can run on many hosts so that it spans regions and data centers. Therefore, for a given database, its transactions engines can run on multiple hosts in multiple regions and in multiple data centers. The purpose of the load balancer is to route SQL connection requests to a transaction engine (TE) that matches certain criteria. NuoDB provides the following load balancer policies:

• RoundRobinBalancer
• ChainableModBalancer
• ModBalancer — This policy is deprecated and is likely to be removed in a future release. Use the ChainableModBalancer policy instead.
• ChainableRegionBalancer
• ChainableReqGroupBalaner
• ChainableTagBalancer
• ChainableLocalityBalancer

You specify a load balancer policy in the default.properties file with the balancer property. The balancer property accepts specification of one load balancer policy, or a comma separated list that lets you specify more than one policy. This is referred to as chaining load balancers. Older (pre-2.1.1) load balancer policies are not allowed to be chained and are noted as such below.

See the following topics: